Large capacity batteries are promising candidates for electric energy storage for electric drive vehicles (EDVs) thanks to their high power and energy density. However, violent incidents reported for this technology, and the consequent safety concerns stemming from such incidents, are still a major hindrance for fast market penetration of large capacity battery powered EDVs. High temperatures can trigger exothermic chemical decompositions of large capacity battery component materials, which then leads to a further increase in temperature and then to a violent failure of the large capacity battery system known as thermal runaway. The unsafe high trigger temperatures may be reached from a variety of failure scenarios including, for example: overcharge of an individual cell or of the entire large capacity battery system; an internal short of cells resulting from a latent defect due to the presence of an internal foreign object, separator wearout, dendrite growth, crush and/or penetration of the cell; an external short of the cell, module or pack; exposure to abnormal high temperature due to failure of neighboring components or fire; and/or combinations of any of the foregoing.
Mature small capacity batteries used in consumer electronics applications ensure safety with multiple redundant layers of incident prevention methods, such as positive temperature coefficient (FTC), current interrupt device (CID), and shutdown separator. Unfortunately, these safety technologies developed for small capacity battery systems do not function properly with large capacity battery systems. The large capacity batteries powering vehicle drive are significantly larger in capacity and physical size than the batteries for personal electronics, and the scaling-up of batteries to large capacity battery systems dramatically changes their behavior under safety incidents such that the safety applications used in small capacity batteries are ineffective with the large capacity batteries scaled up to power EDVs. Large capacity battery systems are typically made by configuring multiple individual cells into a module or a pack both electrically and thermally. Previous attempts to address the anticipated safety issues in large capacity battery systems focused comprehensively at the cell level, and the safety characteristics of large capacity battery systems are often well understood at individual cell level. However, larger batteries, which are a high capacity and high voltage assembly of individual cells, typically change their response greatly to a fault causing unexpected subsequent behaviors. Since pack response is critically affected by pack integration characteristics in a complex relation with the characteristics of unit cells, pack level safety assessment is extremely difficult and expensive in terms of cost and time.
Development of safe large capacity battery systems should include, for example, reliable early detection systems, circuit breaks for excessive currents and reliable shutdown separators, among others. In a large capacity system such as batteries for electric vehicles, detecting a fault signal and confining it locally in a system is extremely challenging. To date, no single system has been developed that has been able to successfully detect fault signals and electrically isolate faults in large capacity batteries.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.